Michael-Dallas

Sounds like low refrigerant.

If you are mechanically inclined (i.e. can do an oil change or brake work), then AutoZone loans out AC vacuum pumps and manifold guages. Very easy to evac, check for leak, and recharge.

Good luck.

Michael.

Chevron Complete Fuel System Concentrate is good stuff. Don't bother with Chevron Fuel Injector Cleaner.

To emphasize what Loren says, my local BMW dealer sells the exact same black Chevron bottle, but a BMW label and part number on it. They charge a couple more dollars more than Chevron from AutoZone. Go figure.

Search the forums on Bobistheoilguy.com and do your research on what's good and what is snake oil.

/m

If it were me, then I'd

1. put the stock exhaust back on and erase the code

2. if the code returns w/ the stock exhaust, then I'd replace the o2 sensors and erase the code

I'm thinking it's either the cats in your aftermarket exhaust or faulty o2 sensor(s).

/m

I kind of have the same problem, but for me, it's getting out of 1st gear. I have to blip the throttle in order to get the shifter out of 1st gear. It seems to happen when it's cold outside.

/m

I suggest folks read this themselves: it is HIGHLY biased towards cross-drilling. AND it does not account for slotted or dimpled rotors or other engineered solid rotors. ONY completely solid ones (see the picture on page 24) and p.23 where they admit they didn't even look at slotted or dimpled rotors). It is unclear what types of venting/vaning the solid rotors they used have - if any!

The article is about the performance effects of cross-drilling rotors and uses solid rotors as a baseline for comparison, that is why slotted or dimpled rotors are not included. If the paper was titled, "The Performance Effects of Rotor Design" then it would make plenty of sense to compare cross-drilling, slotted, dimpled, solid, etc.

Because of these fundamental issues, it is easy to find snippits favorable to cross-drilled rotors in the article - but only as they are compared to generic solid rotors. Again, ONLY completely solid rotors, and not race rotors with slots / dimples / vanes / vents, etc. [Note that there is plenty of discussion about the vaned design of the x-drilled - but almost no discussion on the type or design of the solid rotor. Clearly a Brembo (or other) solid rotor will operate better than less "engineered" models.] Despite the fact that they used junk solid rotors, there were still a number of points favorable to the non-crossdrilled rotors they tested!

Page 3 states that brake system 3b (solid rotors) is identical to 3a (cross-drilled rotors), except 3b rotors were smaller in diameter. Both systems were tested on the same "high peformance sports car." In addition, it states under "Rotor Cooling on Brake System 1":

"of otherwise identical design" -- I think that establishes what kind of solid rotors were used when comparing against cross-drilled rotors in brake system 1.

Also, keep in mind that their test does not accurately represent real world use. For example, the tests were not dramatically affected by pad build up in the holes. This will severely change the results, since the ENTIRE premise of the article is that the holes help. In fact - they indicate that OVER 90% of the hole will clog under use! [brake system 1, full. Brake system 2, 90%.] They also state that this can have really bad results. [This also illustrates that new pad technology does NOT need the holes for venting gas.]

While I don't doubt this point, but is there anybody out there that daily drives their Porsche and has encountered 90% pad build up in the holes? And are the holes for venting gas or cleaning the pad face (like slotted rotors)?

The point I am trying to make is, Porsche selected cross-drilled rotors for specific reason(s). Was it for marketing? Perhaps, but I would be more inclined to believe it if Kia or Hyundai slapped cross-drilled rotors on their mid-sized luxury sedans. But Porsche, Ferrari, Lamborghini, Corvette, GT-R, etc. all have cross drilled rotors, oversized cross-drilled rotors at that. I find it suspect that Porsche would spend years and years on suspension R&D, chassis R&D, engine R&D, tire R&D, fluid R&D only to slap cross-drilled rotors as a complete marketing / bling gimmick.

Are cross-drilled rotors adequate for a pro-am racer running an enduro? Probably not. Are they adequate on an auto that has power mods, track rubber, and/or suspension mods? Perhaps, depending on your driving experience. Are they adequate for a relatively stock car (just pads/fluid) at the track? IMO, absolutely.

///Michael

Hmm, I would have to say that there is a little bit about Porsches(911) being engineered to do 180mph, and Z's set at about 150mph. I would think that sub 12" rotors on a 3300# car would desintigrate after s short time on the Autobahn. Wonder if the specs are different in Europe or Japan? That's an odd comparison. in my book of performance cars, a 350Z you would not find, nor it's competitor the Crossfire or the Z3/4. While they are sporty and 15-26 year olds love them you would more then likely destroy one of them if you did track it(consumer cars). My thoughts on the brakes for 911's is simply engineered to take what you throw at it. Switzerland, Germany, USA, Italy, Doesn't really matter which one. I have run into a few hills in a rental BMW 323 in Garmisch Germany before thart would have really appreciated Porsche brakes.

A short digression...

Well, back in the day, I had a 2003 350z Track model and my friend had a 2003 350z Touring model. My Track model had factory 12.75" rotors front and rear w/ Brembo 4/2 pot calipers while his Touring model had those sub 12" rotors w/ 2 pot sliding calipers.

On our first DE, he had braking issues (heavy pad and fluid fade) while mine held up ok except for the uneven deposition I got on the rotors. I simply had my rotors turned to remove the deposition while he upgraded to a 13" Stoptech BBK. A few DE's later, hairline cracks started developing on my solid 12.75" rotors. At $500 per factory rotor, the 350z Track model quickly lost its allure for a cheap track platform.

Granted that I had the rotors turned to remove the deposition, they were still w/in spec. But if I could crack solid rotors in a few DE's, just think what would happen if I slapped aftermarket cross-drilled rotors w/o increasing rotor width or diameter...

///Michael

Well speak of the devil, my CPO "welcome kit" came in the mail today, which was a little unexpected to say the least! It came with a leather luggage address tag and a shiny CPO keychain. More importantly, there is a booklet that has all nifty tidbits of trivia, one of which included the brakes:

Why are there holes in the brake rotors?

At Porsche we cross drill the rotors on our sports cars to help control their temperature. The cross-drilled holes dissipate water vapor, maximizing contact between the brake caliper and the rotor. They also help the brakes cool faster than a solid rotor. Cooler brakes stop in a shorter distance than hot brakes.

:)

///Michael

How about the Porsche RS Spyder?

No slots or cross-drilling.

How does slotting or cross-drilling affect integrity of those rotors? Maybe in the next decade, those 2 GM engineers will write another white-paper on them... if GM is still around by that time...

///Michael

Now that's a teaser if there ever was one ... without spending $14, what were the high-level

(non-copyright-violating) conclusions ?

Two GM engineers tested 2-3 cross-drilled braking systems and 2-3 solid-face braking systems. The pictures blurred anything on the rotors that could identify the braking systems they tested. It's a 28 page analysis/report with quite a bit of technical mumbo-jumbo.

They made a few observations (including the obvious of cracks developing around the holes), but the one that pertains to my reply is that cross-drilled rotors do improve brake cooling over solid-face rotors. Furthermore, the cooling rate increases as speed increases.

Of course, rotor design also plays an important factor. It is possible to put too many holes in a cross-drilled rotor or place them ineffectively.

The SAE article is locked w/ DRM on my personal laptop. If anybody is interested, then I'll also summarize the other observations that they noted in their conclusion if I get some time this evening. In the meantime, somebody else on another auto forum has read the same paper; you can read his comments as well if you're bored: linky, linky

My personal thoughts is that Porsche designed their cars to use cross-drilled rotors; and what I mean by designed, I mean the rotor diameters for their brakes are oversized. If you took, say a Nissan 350z, a 3300lb car w/ < 12" rotors (at least 2003 non-Track models had < 12" rotors) and bought cross-drilled replacements w/o increasing rotor diameter, then yeah, you're asking for a world of hurt after a few hard track sessions. Another example, the E46 M3 CSL / Competition package has cross-drilled rotors, but they increased the size (diameter & width) of the fronts over your regular M3.

///Michael

IMHO, the holes are there mostly for appearance. Modern pads do some out-gassing when they are first getting bedded in but after that, it's not an issue. The holes may also improve the initial action of the brakes in the wet but in general, braking in the wet is very much limited by tire traction rather than braking force.

There's an interesting white paper from the SAE that may just surprise you: 2006-01-0691, The Effect of Rotor Crossdrilling on Brake Performance.

///Michael